169 votes
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Why are IPv4 addresses running out?

The IPv4 Address Shortage According to Vint Cerf (the father of IP), the IPv4 32-bit address size of was chosen arbitrarily. IP was a government/academic collaborative experiment, and the current ...
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  • 93.5k
82 votes
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Why do we need IPv6?

Two things are getting confused here: classful addressing vs CIDR Masquerading / NAT Going from classful addressing to Classless Inter Domain Routing (CIDR) was an improvement that made the address ...
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40 votes
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What is the difference between 0.0.0.0 and a loopback IP address?

The statement: The IP address 0.0.0.0 [...] means ‘‘this network’’ or ‘‘this host.’’ is misleading. It is not a "or" but "This host on this network." From RFC1122: { 0, 0 } ...
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  • 18.4k
36 votes

Why are IPv4 addresses running out?

Ron Maupin's answer gives a brilliant overview of the IPv4 shortage, but I'd like to address this part of your question: Why can't a city (for example) have just one IP address and all homes in ...
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  • 460
33 votes
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What stops someone from configuring their network with IP addresses they do not own?

Most likely if they're a big university they are their own ISP, using BGP to connect their network to the internet via a number of upstream networks. Nothing stops them from using IP addresses they ...
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  • 15.6k
31 votes
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Why are IP addresses given to each interface and not device? What would the implications of that be?

Connecting an interface to a network makes it a part of that network. Therefore, the IP address is a property of the connection, not the host. Likewise, a host can have many network connections and ...
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  • 70.5k
22 votes

Difference between :: and ::1

:: is the unspecified address (0:0:0:0:0:0:0:0), and it is only used in packets as the source address of a host that does not yet have an address and is trying to get an address assigned. What you see ...
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  • 93.5k
21 votes

How do you calculate the prefix, network, subnet, and host numbers?

Part 1 of 2 IPv4 Math With an IPv4 address and the network mask, the network mask length, or host mask, you can calculate the Network Address, Broadcast Address, Total Addresses, Usable Addresses, ...
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  • 93.5k
21 votes

Does every host on the LAN share the same ARP table, or do hosts keep them individually?

Actually, every interface in a device has its own ARP table. A host could have several ARP tables (one for each interface it has). ARP tables are not shared between hosts, or even among interfaces in ...
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  • 93.5k
20 votes

How do you calculate the prefix, network, subnet, and host numbers?

The answer above hits the nail on the head perfectly. However, when I first started out, it took me a few different examples from a couple of sources for it to really hit home. Therefore, if you're ...
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  • 2,317
20 votes
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What is Link-local addressing?

I never seen 169.254/16 working in IPv4. A PC automatically acquires a 169.254.x.x/16 address if it does not receive an IP address from a DHCP server. If you disable the DHCP server on your home or ...
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  • 2,317
20 votes
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Does anycast addressing add additional latency in any way?

Does anycast addressing, in itself, add any additional latency to network connections? No. one using unicast and the other using anycast Anycast is unicast. It is just that the same network is ...
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19 votes
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Why are there 3 ranges of private IPv4 addresses?

Back when the RFC for private addressing was proposed, classful addressing was still common. The reasons for the three address ranges are found in RFC 1918, Address Allocation for Private Internets: ...
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19 votes
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What are common sizes to split a /29 - /32 IPv6 subnet?

Some simple guidelines that work most of the time: Dividing your /29 The standard size of your allocation from RIPE NCC is a /32 A /32 is a well-accepted prefix size in the global routing table You ...
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18 votes
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IPv4 Segment 100.64.0.0/10

The 100.64.0.0/10 address block is not private address space; it is shared address space. This is spelled out in RFC 6598, IANA-Reserved IPv4 Prefix for Shared Address Space (I highlighted the ...
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18 votes
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What happens when a subnet reaches capacity?

A subnet (network) is really just a collection of contiguous addresses within a binary mask. It is simply a logical way to divide address block. If you run out of addresses in a network (subnet), then ...
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18 votes
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Is there anything stopping me from using Class A addresses on my own network?

As long as you are translating your "15.0.0.0" address space to something unique on the Internet that doesn't overlap, things will "work fine". However, you won't be able to ...
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17 votes

How do you calculate the prefix, network, subnet, and host numbers?

Continued from Part 1... Part 2 of 2 Subnet IPv4 Networks Subnetting a network is creating multiple, longer networks from a network address and mask. The basic idea is that you borrow high-order ...
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17 votes
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Why the first octet of a MAC address always end with a binary 0?

You may notice that two least-significant bits of the most-significant byte of a 48-bit MAC address are usually set to 0 (as in all your examples). There are two flags in the most-significant byte of ...
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  • 93.5k
16 votes

Why are IPv4 addresses running out?

Right now, every home has its own IP address. Why can't a city (for example) have just one IP address and all homes in this city would just be on a private network of that city? Exactly this is ...
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16 votes

Why are IP addresses given to each interface and not device? What would the implications of that be?

It would not be enough. Suppose I have a computer with three interfaces: eth0 (wired Ethernet), wlan0 (wifi), and vboxnet0 (virtualbox). One of the interfaces is connected to an internal network, one ...
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15 votes
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How does DHCP assign an IP address?

The basic process is quite simple. I'll only cover that and omit scenarios where several DHCP servers exist, error conditions crop up or discovery has to cross network boundaries. A new client on a ...
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  • 281
15 votes

Why do we need IPv6?

The Internet Protocol (IP) was designed to provide end-to-end connectivity. The 32 bits of an IPv4 address only allow for about 4.3 billion unique addresses. Then you must subtract a bunch of ...
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  • 93.5k
15 votes

Why do we need MAC Address if we can uniquely identify each machine with an IP Address

There is a historical reason for this, as @ronmaupin alludes to. In small networks, you don't need a layer 3 protocol. All the devices are directly addressable, so layer 2 addresses work fine. As ...
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  • 62.4k
14 votes

Setting subnet mask to 255.255.255.255

Yes, there's a problem. Your default gateway needs to be in the same subnet as your device. By setting the subnet mask to 255.255.255.255, you've told the computer that nothing else is in its subnet....
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14 votes
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What would happen to Ping if two PCs have same IP address with same Subnet Mask on same network?

Actually, the ping gets sent to a layer-2 address if they are on the same LAN. Assuming ethernet, the sending host may have a MAC address in its ARP cache, and the pings gets sent to the host with ...
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  • 93.5k
14 votes
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How do routers on the backbone avoid IP address conflicts?

The RIRs assign addressing to the ISPs. An ISP not following the rules will quickly find itself ostracized and cut off from the rest of the Internet. IANA owns the addressing and assigns each of the ...
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  • 93.5k
12 votes
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Which CIDR block contains the most IP addresses, 192.168.0.0/16 or 169.254.0.0/16?

These IP blocks contain exactly the same number of IP addresses. An IP is made of 4 bytes, separated by dots. Each byte can take (theorically) the value from 0 to 255, meaning 256 different values, ...
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12 votes

What stops someone from configuring their network with IP addresses they do not own?

What stops them from attributing their routers and hosts already in use IP addresses? Nothing. Over the years, I have seen both organizations of all sizes, both public and private, do this including ...
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